This invention relates to novel cationic compositions and to methods of making and using the same. In preferred embodiments, the present invention relates to cationic compositions and methods which contribute to the reduction of hazardous waste production in photo-imaging and stereolithography
The production of hazardous waste in the area of photoimaging can be related to several root causes. One of these causes can be poor image resolution at the edges of the imaging region. Poor image resolution can result in wasted hazardous materials. By improving diffusional resolution of such products, it is possible to reduce the volume of waste produced in various imaging processes. A second cause has been the lack of commercially viable non-hazardous compositions.
Within the field of stereolithography, cationically and mixed cationic/free radical (hybrid) formulations are utilized. Many cationic and hybrid formulations utilize initiators that include antimonate salts. Use of more environmentally friendly and in some cases non-hazardous constituent cationic initiators, for example phosphorous-based cationic initiators, has been undesirable primarily due to poor cure speed but also, in part, due to poor diffusional resolution. There are many factors that are believed to contribute to undesirable diffusional resolution including slow cure speeds and diffusion of activated materials from the image region.
U.S. Pat. No. 6,787,286 Szmanda et al. describes photoresist formulations where the solids content of the composition varies between about 5 and 35 percent by weight of the total weight of the photoresist composition, and more typically 5 to about 12 or 15 weight of the total weight of the photoresist composition, in which it is suggested that some degree of photoacid diffusion is affected by use of a basic additive.
U.S. Pat. No. 6,165,386 Endo et al. describe the use of Kayacure BMS ([4-methylphenylthio)phenyl]phenylmethanone) as a photosensitizer for free-radical formulations. Likewise a product brochure by Chitec, “Additives for UV Curing, Photoinitiator & Photosensitizer”, describes use of Chivacure® BMS (4-Benzoyl-4′-methyldiphenyl sulfide) as a sensitizer for free radical systems.
U.S. Pat. No. 5,474,719 Fan et al. describe a stereolithography process wherein excess composition is removed using an air knife in order to form uniform layers of composition during part fabrication.
The present invention is embodied broadly in cationically curable compositions comprising a cationically curable component, a cationic initiator; and at least one of (i) a photosensitizing effective amount of a benzoyl diphenyl sulfide compound, or (ii) a photoacid diffusion inhibiting effective amount of a fluorinated surfactant.
In especially preferred embodiments, the compositions of the invention will comprise both the photosensitizer and the fluorinated surfactant.
One especially preferred cationically curable composition of this invention will comprise (a) a cationically curable component, (b) a cationic initiator; (c) a benzoyl diphenyl sulfide compound, and (d) a fluorinated surfactant.
Preferred embodiments will include a photosensitizer having substantially no light absorption above 400 nm and an extinction coefficient of 300 liters/mole-cm or greater. The photosensitizer is most preferably present in an amount to provide a depth of penetration (Dp) of between about 0.01 to about 0.03 cm. Exemplary embodiments will employ the photosensitizer in amounts between about 0.01% to about 1.0% by weight of the composition exclusive of filler weight. Most preferably, the photosensitizer employed in the compositions of the present invention will comprise 4-benzoyl-4′-methyldiphenyl sulfide (sometimes more simply referenced below as BMS).
In other embodiments of the invention, the compositions will comprise a fluorinated surfactant in an amount of between about 0.0001 wt. % to about 5 wt. %. In some embodiments of the invention, the compositions will include a fluorinated surfactant which contains at least one fluorinated moiety CpFm, where p is from 1 to 4 and m is from 3 to 12. Preferably, the fluorinated surfactant is a fluorinated ether.
In other embodiments of the invention, the fluorinated surfactant is at least one selected from the fluorinated surfactants of Structure 1 and Structure 2:
wherein n is 6 or greater. Preferably n is lower then 100.
The cationically curable component employed in embodiments of the invention preferably comprises at least one of epoxide-containing compounds, and hydroxyl-functional compounds. In another aspect, the compositions of the present invention will further comprise an oxetane. The compositions of the present invention in yet another aspect may include (meth)acrylate compounds.
In another aspect, the compositions of the invention may comprise at least one cationic initiator selected from the group consisting of iodonium compounds and sulphonium compounds. In preferred embodiments, the iodonium compound may comprise (tolylcumyl)iodoniumtetrakis(pentafluorphenyl)borate.
In another aspect, the present invention is embodied in a method of forming a cationically cured material comprising subjecting the cationically curable composition to cationic curing conditions for a time sufficient to form a cured material therefrom. Especially preferred embodiments of the invention are methods of forming a three-dimensional article by means of stereolithography by (1) coating a layer of the cationically curable composition as described herein onto a surface; (2) exposing the layer imagewise to actinic radiation to form an imaged cross-section, wherein the radiation provides sufficient exposure to cause substantial curing of the layer in the exposed areas; (3) coating a layer of the composition onto the previously exposed imaged cross-section; (4) exposing the layer from step (3) imagewise to actinic radiation to form an additional imaged cross-section, wherein the radiation is of sufficient intensity to cause substantial curing of the layer in the exposed areas and to cause adhesion to the previously exposed imaged cross-section; and (5) repeating steps (3) and (4) a sufficient number of times in order to build up the three-dimensional article.
This invention also provides for reducing the production of non-hazardous, hazardous or hazardous constituent wastes from use of photocurable cationic compositions. In one aspect, this waste reduction is achieved by improving the imaging of a cationic composition, such as by improving the diffusional resolution and/or the layer formation of such compositions by including photoacid diffusion inhibitors in the composition. By improving the diffusional resolution of such compositions, there is less waste produced and greater composition reuse potential in applications such as stereolithography. In particular, the disclosed methods and compositions can be useful in fabricating, for example, molds using stereolithography that can be used in vacuum molding processes for the production of thermoplastic articles.
In one embodiment, a high solids cationic composition for use in photoimaging applications and for reducing waste can include a photoacid diffusion inhibitor.
In another embodiment a method of improving diffusional resolution in a high solids cationic composition for photoimaging can include limiting diffusion of a photoacid in the composition. This can be accomplished by forming an association between a cationic photoinitiator and a photoacid diffusion inhibitor.
In another aspect, a method of reducing waste from stereolithographic processes can include mixing a photoacid diffusion inhibitor with a stereolithographic composition.
Another aspect includes a mold for production of articles that includes a cationic composition and a photoacid diffusion inhibitor. In another aspect, a method of producing molded articles can include forming a mold using a cationic composition and forming a thermoplastic film using the mold.
In yet another aspect, a stereolithographic composition can include a high solids composition and a fluorinated polymer, where the stereolithographic composition is non-hazardous.
In another aspect, a cationic composition for reducing waste production can include an oxetane, and a boron-containing, cationic photoinitiator or a phosphorous-containing cationic photoinitiator. The composition can be antimony-free. The composition can also include epoxides such as glycidyl epoxides, (meth)acrylates, hydroxyl-containing compounds and any combinations thereof. The composition can have no significant absorbance above 400 nm. The composition can also include a free radical initiator. In another aspect a method of reducing waste production from stereolithographic processes can include curing a portion or all of a cationic composition.
In another aspect, a method of cleaning stereolithographic articles can include removal of excess stereolithographic composition from the articles using an air knife or using liquid or supercritical CO2.
In yet another aspect, a method of forming stereolithographic articles can include forming an article from a high solids cationic composition, removing excess composition material from the formed article, separating, such as by filtering or using centrifugation or another form of centrifugal force, the removed excess material and recycling the removed excess material.